Certain types of gas analyzers employ a sample cell into which gas to be analyzed is pumped. Energy is passed through the gas in the sample cell, for example using an infrared beam, and the effect on the energy is analyzed to determine the concentration of constituents of the gas in the sample cell.
A gas analyzer of the general type described above is an automotive exhaust gas analyzer. An example of an automotive exhaust gas analyzer is shown and described in U.S. Pat. No. 4,687,934. Such gas analyzers measure the presence of carbon monoxide, carbon dioxide and various hydrocarbons, which are typical constituents of automotive exhaust gas.
Engine exhaust emissions contain coarse and fine particulate matter, water in both liquid and vapor phase, other condensates, gaseous hydrocarbons, carbon monoxide, carbon dioxide, oxides of nitrogen, oxygen, and other compounds. Contaminants must be filtered out by a series of different filters, each suited for the particular contaminant in order to accurately measure the remaining constituents of the gas. The general filtration process involves first removing large particles, liquid water, and other condensates using a relatively coarse filter stage. The condensate can be filtered by another finer filter stage before being drawn off by a pump. The filtered gas can also be filtered for finer particles (typically less than 5 micron particles) by another filter stage. In particular, the removal of water before the final filter stage is important because water absorbs the hydrocarbons which is one of the classes of gases to be analyzed. If water is present in the final filter stage, the hydrocarbon measurements will be inaccurate. Further, certain structural materials can adsorb molecules to be analyzed. These adsorption phenomena can deleteriously affect the accuracy of the analyzer. Thus, the filtration process is extremely important for accurate measurements of gas constituents and to protect the analyzer and pumps.
A particularly useful filter assembly for a gas analyzer is shown and described in U.S. Pat. No. 5,049,170 Sep. 17, 1991 and assigned to the assignee of the present invention. One of the significant advantages of the filter assembly shown and described in the aforesaid patent is its relatively low void volume. This produces increased accuracy by minimizing the amount of surface area to which hydrocarbons can adhere, and requires a modest pump flowrate with attendant advantages.
The presence of large amounts of condensate, puddles of liquid in the exhaust system, careless placement of the intake probe, etc., can, on occasion, result in a large and sudden intake of liquid into a gas analyzer system. Filter assemblies which are of low volume to improve accuracy of hydrocarbon measurements, such as the filter assembly described in the above referenced patent, may become flooded or overwhelmed by the sudden intake of liquid, rendering the analyzer system inoperable. It is a general object of the invention to provide an improved filter system for a gas analyzer.
A more specific object of the invention is to provide an improved filter system for a gas analyzer which prevents the flooding or overwhelming of the gas analyzer as a result of a sudden rise in liquid intake into the filter system.
A further object of the invention is to provide an improved gas analyzer wherein flooding or overwhelming of the analyzer is prevented in a low cost and expedient manner.
Other objects of the invention will become apparent to those skilled in the art from the following description, taken in connection with the accompanying drawings.